Dosage forms for delivering a drug to a biological environment of use are known to the prior art in U.S. Pat. Nos. 3,845,770 and 3,916,899, issued to the patentees Felix Theeuwes and Takeru Higuchi. The dosage forms disclosed in these patents comprise a wall that surrounds an internal compartment containing the drug. The wall is permeable to the passage of an external fluid and it is substantially impermeable to the passage of drug. There is at lease one passageway through the wall for delivering the drug from the dosage form. These dosage forms release the drug by fluid being imbibed through the wall into the compartment at a rate determined by the permeability of the wall and the osmotic pressure gradient across the wall to produce an aqueous solution containing drug that is dispensed through the passageway from the dosage form. These dosage forms are extraordinarily effective for delivering an agent that is soluble in fluid imbibed into the dosage form that exhibits and osmotic pressure gradient across the wall against an external fluid.
A pioneer advancement in dosage form invention was presented to the drug delivery arts by Richard Cortese and Felix Theeuwes in U.S. Pat. No. 4,327,725. The invention disclosed and claimed in this patent pertained to enhancing the delivery kinetics of the dosage form for delivering drugs with various degrees of solubility in aqueous fluids that are difficult to deliver, by manufacturing the dosage form comprising a hydrogel. The hydrogel in the presence of fluid imbibed into the dosage form, swells and moves from a rested state to an expanded state. The force generated by the expansion of the hydrogel is applied against the drug thereby pushing the beneficial drug through the passageway from the dosage form.
The dosage forms provided by the prior art operate successfully for their use, and they can deliver numerous drugs. Now, it has been found that some hydrogels used in these dosage forms often exhibit an unwanted effect on the drug, that causes it to lose its chemical integrity and therapeutic activity. That is, the drug may decompose and consequently the intact drug is not available for delivery from the dosage form.
In light of the above presentation, it will be appreciated by those versed in the dispensing art to which this invention pertains, that a pressing need exists for a rate controlled dosage form that can deliver a drug intact to a patient in need of therapy. It will be appreciated further by those versed in the delivery arts, that if a dosage form is provided comprising a hydrogel that can deliver a drug substantially-free of the unwanted effects of the prior art, such a dosage form would have a positive value and it also would represent both an improvement and an advancement in the dispensing arts.